Extreme ultraviolet photolysis of CO₂ - H₂O mixed ices at 10 K

Experimental results on the spectral identification of IR absorption features and the production and depletion column densities produced through EUV photolysis of H₂O + CO₂ (4:1) mixed ices at 10 K are reported. A tunable intense synchrotron radiation light source was employed to provide the required high flux EUV photons. In this study the photon wavelengths used to irradiate the icy sample were selected to coincide with the prominent solar lines at 58.4 nm and 30.4 nm. A FTIR spectrometer was employed to obtain the in situ IR absorbance spectra produced through EUV photolysis of a given ice sample. Photon-induced chemical reaction products were primarily H₂CO₃ and CO. While new molecular species were formed, the original reactants were depleted, as expected. We report the yields for producing H₂CO₃ and CO and the yields for depleting the parent CO₂ molecule through EUV photolysis of the mixed ices. We have searched for possible intermediate products H₂CO and HCO, but could not positively identify their existences in the spectra. The results presented in this work are particular relevant to our understanding of chemical evolution and synthesis in H₂O-rich icy satellites of the giant planets, comets, the interstellar medium, molecular clouds, and protestellar regions.